The present invention relates, generally, to microvalves, and in particular to an improved microvalve device configured to provide a more robust and durable operation to withstand the demands of various operating environments.
Micro Electro Mechanical Systems (MEMS) are an emerging technology used to fabricate working mechanisms on a micro-miniature scale. Typically MEMS devices can be divided between two categories: sensors and actuators. MEMS sensor devices include, for example, the accelerometers used to deploy airbags, pressure sensors, and even chemical sensors. MEMS actuator devices can be configured for applications such as, for example, fluid flow control in microvalves or the control of optical signals utilizing micromirrors and other like devices.
MEMS valves comprise micro-fabricated devices typically having a size of a few xcexcm to a mm and which are configured to admit, restrict or block the flow of fluid, including air, gas and liquid. Typically, existing microvalve devices suffer from various problems, including a lack of robustness and durability, or quite often from insufficient fluid flow properties, such as flow rate, operating pressure, and limitations on the types of fluid that can be used (e.g., most microvalves only admit air). More recently developed microvalves, including gate valve designs and diaphragm designs, have attempted to address the above problems.
Microvalves using a diaphragm design actuated by the pressure differential across both sides of the diaphragm, for example, valve 100 illustrated in FIG. 1, generally comprise a cover plate 101, a valve plate 102 having a diaphragm 103, a control gate 104 with a closure plate, and a lower substrate 106. Diaphragm valve 100 uses a pressure differential across both sides of diaphragm 103 to produce the movement of diaphragm 103 in order to block or free the fluid passage way. The pressure differential is regulated by control gate 104 by activation of the closure plates to regulate the pressure differential through controlling the pressure within a pressure control chamber 108.
While providing more durability and potentially less power consumption, such pressure balance microvalves usually offer a nonlinear response, provide a poor flow rate performance, require additional wafer bondings, and are more costly to manufacture. For example, because of the structure of diaphragm 103, a large differential pressure is generally necessary to actuate pressure balanced valve 100. In addition, due to the structure of diaphragm 103 and the flow passageway, the available flow rate is limited. For example, due to a steeply inclined boss component on diaphragm 103, fluid flow through the passageway from the inlet orifices to the outlet orifices produces nonlinear flow characteristics, as well as cavitation. Such a steeply inclined boss component is mainly due to current bulk-micromachining techniques currently available, which limit the slope of the boss component to 54.7xc2x0 angle of inclination. Moreover, in that pressure control chamber 108 is regulated by the small control gate 104, typically comprising a gate or bimorph-type valve, leaks within control gate 104 often occur, i.e., control gate 104 may not always maintain the pressure (P+xcex94P) necessary for regulation and control of diaphragm 103. Further, in that the mechanisms for actuation for microvalve 100 are configured proximate to, or a part of, the components of microvalve 100, such as control gate 104, such a microvalve configuration unfortunately exposes the mechanisms for actuation to any fluids used within the flow passageway, such as to intermix electrical signals with conductive fluids. Still further, in that such pressure balanced microvalves generally require wafer bondings, the manufacture costs are generally high.
Other newly developed microvalves employ a gate valve design which comprise moving gates on the surface of a silicon substrate with orifices. For example, with reference to FIGS. 2A and 2B, a gate valve 200 has a gate 202 comprising a nickel flap that is actuated to move horizontally on the surface of a silicon substrate 203 which contains through orifices 204 in order to regulate flows directly. Gate 202 can include a shutter configuration 202A, or other configurations of openings, which permit regulation of air flow. In addition, gate valve 200 generally provides a greatly increased flow rate, has a faster response, and is more cost effective to fabricate than the pressure balance microvalves.
However, gate valves also have various deficiencies. For example, due to a typical polysilicon thermal actuator design, to actuate gate 202 to open or close valve 200, a large voltage is necessary, often comprising 30 volts or more. In addition, because of the microelectronic fabrication process of such microvalves, gate valves typically realize leak flow, even despite the application of electrostatic clamping devices. For example, on many occasions, the leak flow can be as high as 10-20% of the overall flow rate, and even worse on other occasions. Further, the appearance of leaks increases as the pressure of the fluid increases. Probably most problematic, due to their unidirectional flow characteristics, these gate valve designs are limited in their capability to withstand back pressures produced during their operation while interfacing with other output devices. For example, any back pressure, for example as little as 10 psi, that may be present in such a device will tend to bend the metal flap and thus fatally and permanently damage it. These back pressure problems result in leaks in the gate valve, even despite the application of electrostatic clamping devices. Still further, gate valves cannot effectively operate with a conductive fluid, e.g., water and the like, because the electronic-based actuation circuit is exposed to the conductive fluid.
Therefore, as one skilled in the art will appreciate, there exists a need for an improved MEMS microvalve device that is more robust and durable to withstand the demands of various operating environments while providing uni-directional and bi-directional fluid flow capabilities, and yet is still cost effective to manufacture.
A microvalve according to the present invention addresses many of the shortcomings of the prior art. In accordance with various aspects of the present invention, an improved microvalve device is configured to provide a more robust and durable operation to withstand the demands of various operating environments. In accordance with an exemplary embodiment of the present invention, a microvalve may comprise a valve seat and a diaphragm, with the diaphragm operated by an external actuator device through various mechanisms of actuation that are separate from the microvalve. Through use of the various mechanisms of actuation, the actuator device is configured to apply forces on the diaphragm to suitably move the diaphragm to open and close the microvalve. For example, an actuation mechanism may apply force actuated through use of an external actuator device, such as a bladder device, to move the diaphragm as intended.
In accordance with another exemplary embodiment of the present invention, the valve seat and diaphragm can be configured to provide the microvalve with a plurality of openings configured to permit flow thereinbetween. In addition, the microvalve may be configured to facilitate uni-directional or bi-directional flow. Further, in accordance with other exemplary embodiments, a plurality of microvalves can be cascaded together in a parallel and/or series configuration, with each valve having similar or different flow characteristics, and being selectively operated.
In accordance with another aspect of the present invention, the external actuator device can be suitably actuated by various means, including by direct mechanisms such as electrostatic, electromagnetic, piezoelectric, and/or by indirect mechanisms, such as thermal actuation, or by any other similar means. The separation of the mechanism of actuation from the design of microvalve mechanisms provides great flexibility in implementation of the microvalve in various applications. Such a separation of actuation mechanisms from the valve design facilitates the providing of microvalve fluid passageways without obstruction, thus resulting in increased linear flow characteristics with respect to the actuation and pressure of fluid. In addition, the separation of actuation facilitates the selection of suitably actuation mechanisms to meet the requirements with respect to response time, frequency response, applied forces, space considerations, and other design considerations. In addition, while typical microvalves are configured to work with only air, through separation of the mechanism for actuation, e.g., the separation of the fluid passageway from the actuator device, the exemplary microvalves of the present invention can operate with various types of fluids, including air, gas and liquids.
In accordance with another exemplary embodiment of the present invention, the microvalve can also include a combination gate valve configuration and a bladder configuration to provide high frequency response characteristics in addition to stability and reduction in leak flow. The gate valve can comprise various metals and other materials, such as ceramic, glass or other like materials.